This invention concerns a device to grind mill rolls and/or pinch rolls in-line.
The invention is applied particularly, but not only, in finishing rolling trains used in plants to produce strip, sheet and/or wide plate.
In rolling plants for strip, sheet and/or wide plate, one of the most important problems which operators in the field complain of is the progresive deterioration, during the rolling cycle, of the surfaces of the working rolls and the support rolls and/or intermediate rolls, and also the surface of the pinch rolls.
For it is well-known that the effect of friction, caused by the rolling process, between the material being rolled and the rolls themselves, causes a progressive wear on the surface of the rolls, both in terms of roughness of the working surface and in terms of the longitudinal profile of the surface.
In hot rolling, apart from the mechanical effect caused by this friction, it is necessary to consider and add the effect of the rapid and ample thermal cycles to which the surface of the rolls is subjected with every revolution of the roll.
The unevennesses which are produced on the surface of the working rolls cause a deterioration in the quality of the surface of the product, both in terms of finish and in terms of the transverse profile obtained which is not the one desired.
This deterioration becomes progressively more marked until it becomes necessary to substitute the worn rolls, whose surface is then ground off-line so that the rolls can be used again.
Since the speed at which the surface of the rolls deteriorates increases in proportion to the progress of the deterioration itself, it becomes necessary to substitute the rolls frequently not only to maintain the surface quality of the product at sufficient and acceptable levels but also to extend the working life of the rolls and therefore limit the wear, as the cost of the rolls is a considerable factor in the total cost involved in the working of the product.
These considerations may be extended to the pinch rolls, which are normally present on the rolling lines downstream of the stands and upstream of the winding reels.
The problem of the progressive deterioration also concerns the support rolls which, in the so-called four high rolling stand, are arranged in cooperation with a relative working roll and in contact with it.
The variation in the longitudinal profile of the support roll caused by wear causes a deformation of the axis of the relative mating working roll, and an unwanted modification of the gap between the working rolls, which causes a further worsening of the quality of the product being rolled in terms of the transverse profile.
From what we have said above, it is clear that the rolls, and particularly the working rolls, need to be replaced frequently, which however requires the line to be stopped and therefore a reduction in production with consequent increases in the cost of working the product.
In order to try to solve these problems various solutions have been proposed to overhaul the surface of the rolls and the pinch rolls by means of so-called in-line grinding, using grinding devices arranged in cooperation with the surface of the various rolls.
Grinding devices known to the state of the art are composed of a plurality of idler grinding wheels set obliquely with respect to the axis of the relative roll. These grinding wheels are made to rotate by the contact with the rolls, generally at a limited speed, as in U.S. Pat. No. 4,716,687.
Another solution is to include a series of coaxial grinding wheels brought into rotation by a common or differentiated drive device as in EP-A-0,672,470.
Other solutions known to the state of the art include grinding wheels or grinding tools thrust against the rolls by autonomous pressure means as in EP-A-0.154.319.
However it must be pointed out that the wear on the rolls is not uniform along the circumference, it has localised depressions; this means that the quantity of material to be removed varies, even considerably, during the grinding step along the same generating line of the roll.
Consequently, in-line grinding devices known to the state of the art have the disadvantage that they do not carry out a differentiated grinding action according to the circumferential areas of the roll on which they are working.
A further disadvantage of the grinding devices known to the state of the art is that the grinding wheels, or parts of the grinding wheels, may have a differentiated wear, as a consequence of the greater or lesser quantity of material removed, and this causes a differentiated reduction in the diameter.
As a consequence, the grinding is not uniform on the circumference of the roll and therefore the final result is unsatisfactory.